My question is based on the experience in the last few days and the various tests I have done.

I observed that if I do not read and simply delete some email which I had automatically put under some particular label using a filter, Gmail starts branding them as spam. See this one.

Gmail started putting these here since once I did not read the emails under this label and deleted them all. Similar cases happen to other group emails under other labels, which sometimes I do not read and delete when I do not have the time. (The label you can see was automatically added by the filters I created.)

Now, if I update the filter for that label and set the check box Never send it to Spam, Gmail will slacken its burden on these ones, only to target new ones. I find that it starts sending emails to spam, which were never before sent to spam. I know that I am being somewhat nonspecific here in the last statement, but that is the best I can do. When I updated all my labeling filters and painstakingly set the Never send it to Spam for all the groups labels, Gmail targeted others, which, again, were never sent to spam before.

I understand that Gmail spam filtering process is not very public knowledge. As my knowledge goes, the catcher will have to use some complex set of rules. We find only some partial information (1, 2, 3) on Gmail spam filter.

Is there some kind of quota the spam filter/catcher needs to fulfill per day?

Maybe the question sounds borderline funny to you, but as I see, if I do not allow it to catch some, it will catch others.

Is there a way I can ask Gmail spam catcher to be a little less aggressive?

I started using Gmail for its spam filtering ability (along with some other wonderful features), but now I feel that it is overdoing sometimes.

1 Answer
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Clearly there is no daily quota - unless my experience is untypical. It can be months before even a single one of my Gmail items is sent to Spam. I have been careful about disclosure of my Gmail address (I use an address at a different service provider when obliged to provide such a means of contact to those I do not fully trust. I have even set up a temporary account at a third service provider for a contact I did not trust at all.)

As you mention, the general public does not know all the details of how Gmail decides what to treat as spam. What we do know, or can predict with reasonable certainty, is that a lot of the factors taken into consideration are to do with the message itself or the sender - not the recipient. For example blacklists of sources, content analysis (including Subject, other 'header' details, multiple addressees), frequency of submissions and spam reports.

A recipient can do little to affect this other than to report as spam (no use to you when you want less aggressive treatment) or, probably, to delete without opening the mail.

So I suggest you either "Mark as read" before deletion, or you open emails before deleting those from people you do not want to be treated as potential sources of spam. Moving them (even if unread) to a folder (other than Spam!) prior to deletion might help.